This invention relates to method and apparatus for installing of cables on poles through aerial conduit, and more particularly to aerial installation of long runs fiber optic, television and other communication cables.
Applicant R. C. Langston has previously been granted U.S. Pat. Nos. 5,029,816; 4,875,661; 4,757,976; 4,669,705 and 4,576,362 on methods and apparatus for installation of fiber optic and other forms of cable in underground conduit, using a novel system of large-diameter narrow capstan assist winches to relay long runs of cable through conduit with minimal splicing and risk of damage to the cable. The teachings of these patents are incorporated by reference herein and are improved upon and specially adapted, as disclosed herein, for aerial installation of long runs of cables in conduit on poles.
In the prior art, the difficulties of aerial installation of cable on poles include lashing the cable to metal strand with metal wires; kinking or over-bending the cable; and inability to handle long runs of cable. Commonly, the cables are installed on existing power poles which have a longer spacing than between or telephone poles. The poles are often unequally spaced and often are positioned out of a straight line so that the cable must bend around angles including 45 and 90 degree angles. The power companies prefer that any communication cable hung on their poles sag in the same manner as the power lines.
Lashing the cable to metal strand with metal wires does not allow the cable to move adequately and to adjust adequately to temperature changes. Conventional practice is to tension the strand as tightly as possible and then lash the cable to the metal strand without tension on the cable. This is inconsistent with power company wire-tensioning practices and runs the risk of the power lines and supporting strand contacting the communication cable as temperature changes vary the relative sags of the lines. Conventional methods of connecting cable to poles, by lashing the cable to the strand which is affixed by bolts to the poles, does not permit the cable to move lengthwise with temperature changes and can cause kinking or over-bending of the cable at 45 to 90 degree bends.
In an attempt to solve these problems, others have tried to use interduct or conduit to contain and support the cables by lashing the interduct to the metal strands. This approach introduces a new set of problems, including difficulties in installation, cable freezing problems, and the need for more splices in the cable than in the prior metal wire lashing techniques. At the same time, it does not really solve the problems of stretching, kinking or over-bending the cable.
The current method of installing cable in interduct or conduit is to split the interduct lengthwise and insert the cable in the interduct using a special tool as the cable and interduct are fed off of adjacent reels mounted on service truck. Meanwhile an aerial lift on the truck carries the combined cable/interduct upward over rollers onto the poles to be lashed to the strand. The first problem arises when an obstacle is encountered, such as a down guy wire or telephone or TV line drop or a power drop to an underground feed, that does not allow the truck and combined cable/interduct to pass. In this case, either the reels must be lifted over the obstacle using a crane or the combined cable/interduct must be cut and respliced around the obstacle. Both of these alternatives are time-consuming and expensive. Splicing is the most common approach but adds to dB losses in the cable and presents a point of probably future problems in cable operation. It would be preferable to be able to install long unbroken runs of cable in aerial conduit.
The conventional method of aerial installation of combined cable/interduct risks damage to the cable by over-bending or kinking it both during installation, as the combined cable/interduct is allowed to sag as it is being strung, and also on a continuing basis once it is strung and lashed onto strand where it must make a 45 to 90 degree bend at a pole. The interduct provides some protection to cable as it is installed but is not sufficient alone to prevent over-bending of the cable where it makes a bend when mounted on a pole. This especially increases the risk of damage to fiber optic cable. When the combined cable/interduct is bent at an angle, the cable is stretched taut at the bend and binds in the bend in the interduct so that it cannot move freely to accommodate temperature changes. Over time this will stress and ultimately damage the cable, particularly in the case of fiber optic cable.
Previously, others have installed aerial cable in unsplit interduct by pulling relatively short lengths (5,000 to 8,000 feet) of cable into the interduct using a conventional end puller. This approach has the drawback of requiring too many splices and is slower than the split interduct method Another little recognized problem is that the interduct can admit water and condensate at its ends which, if frozen, could damage the cable. Consequently, the approach of pulling cable into unsplit interduct has not been widely used. As previously used, this approach does not solve the bending and movement problems.
Accordingly, there remains a need for a better way to quickly and efficiently install long runs of aerial cable on poles and the like.